As for copper alloys for electronic materials used in various electronic parts such as connectors, switches, relays, pins, terminals, lead frames etc., it is desired to satisfy both high strength and high electrical conductivity (or thermal conductivity) as basic properties. In recent years, high integration as well as reduction in size and thickness of electronic parts have rapidly advanced, and in correspondence with the foregoing advancements, the desired level for copper alloys used in electronic device parts are becoming increasingly sophisticated.
In regards to high strength and high electrical conductivity, the amount of precipitation hardened copper alloy used as the copper alloy for electronic materials, in place of solid solution strengthened copper alloys such as conventional phosphor bronze and brass, have been increasing. In precipitation hardened copper alloys, microfine precipitates uniformly disperse by age-treating of a solutionized supersaturated solid solution to increase alloy strength, and at the same time the amount of solutionized element in copper decrease to improve electrical conductivity. As a result, a material having excellent mechanical characteristics such as strength and spring property as well as good electrical and thermal conductivity is obtained.
Among precipitation hardened copper alloys, a Ni—Si copper alloy generally referred to as the Corson alloy is a representative copper alloy that possesses the combination of relatively high electrical conductivity, strength, and bending workability, making it one of the alloys that are currently under active development in the art. In this copper alloy, improvement of strength and electrical conductivity is attempted by allowing microfine Ni—Si intermetallic compound particles to precipitate in the copper matrix.
In order to improve further properties of the Corson alloy, various technical developments such as addition of alloy components other than Ni and Si, exclusion of components that adversely affect properties, optimization of crystalline structure, and optimization of precipitation particles have been performed. For example, properties are known to be improved by addition of Co or by controlling second phase particles precipitating in the matrix, and recent improvement technologies on Ni—Si—Co copper alloys are listed below.
Japanese Translation of PCT International Application Publication No. 2005-532477 (patent document 1) describes controlling the amounts of Ni, Si, and Co and the relationship thereof in order to obtain Ni—Si—Co copper alloys having excellent bending workability, electrical conductivity, strength, and stress relaxation resistance. Average grain size of 20 μm or less is also described. The manufacturing step thereof is characterized in that the first age annealing temperature is higher than the second age annealing temperature (paragraphs 0045-0047).
Japanese Published Unexamined Patent Application Publication No. 2007-169765 (patent document 2) describes controlling coarsening of crystal grains by controlling the distribution of second phase particles in order to improve the bending workability of Ni—Si—Co copper alloys. In this patent document, for a copper alloy having cobalt added to the Corson alloy, the relationship between precipitates having the effect of controlling coarsening of crystal grains and its distribution in high temperature thermal treatment is clarified, and strength, electrical conductivity, stress relaxation property, and bending workability are improved by controlling the crystal grain size (paragraph 0016). The crystal grain size is the smaller, the better, and a size of 10 μm or less is said to improve bending workability (paragraph 0021).
Japanese Published Unexamined Patent Application Publication No. 2008-248333 (patent document 3) discloses a copper alloy for electronic materials having controlled generation of coarse second phase particles in the Ni—Si—Co copper alloy. This patent document describes that controlling the generation of coarse second phase particles by hot rolling and solutionizing under particular conditions will allow for realization of the target superior property (paragraph 0012).    Patent Document 1: Japanese Translation of PCT International Application Publication No. 2005-532477.    Patent Document 2: Japanese Published Unexamined Patent Application Publication No. 2007-169765.    Patent Document 3: Japanese Published Unexamined Patent Application Publication No. 2008-248333.